Randomly oriented ZnO nanowires grown on amorphous SiO2 by metal-catalyzed vapour deposition

Randomly oriented ZnO nanowire (NW) networks have been grown on thermal SiO2 substrates by the simple carbothermal reaction-assisted thermal evaporation of ZnO. One-dimensional growth was achieved with the aid of Au nanocluster catalysts dispersed on the substrates. The structures were studied by scanning electron microscopy, energy dispersive X-ray analysis, and X-ray absorption spectroscopy. The NW diameters and lengths were found to strongly depend on the substrate temperature (TS) and to be in the 5-10 nm and 40-110 nm ranges for TS = 520 oC, and in the 50-80 nm and 1-3 μm ranges for TS = 700 oC, respectively. The growth regime was characterized by comparing the NW structures obtained on SiO2 with those grown in the same deposition run on (1 0 0) Si substrates also covered with the Au catalyst. The NW structure prepared at 700 oC behaves as a dense NW network with net electrical conductance and persistent photoconductance. These results suggest a method to deposit size-controlled ZnO NW networks on insulating cost-effective substrates with important potential applications as in chemical sensors and solar cells.